The present invention relates to a magnetic disk apparatus and a storage system which is mounted with the same, and more particularly, to a magnetic disk apparatus suitable for mobile applications such as a portable information terminal, and a storage system which is mounted with the magnetic disk apparatus.
Conventionally, cameras, tape recorders, projectors, video recorders, and voice recorders have been used for aiding persons in memorization, while personal computers (PC), portable digital assistants (PDA) and the like have been used as a system for recording and reproducing a variety of documents such as pictures, movies and voices. These devices can record what a user has viewed and heard on a recording medium and reproduce it as required to restore the originally acquired information as it is. These devices generally start recording in response to a manipulation deliberately made by the user for “recording.” In many cases, magnetic tapes and semiconductor memories are used as recording media.
For aiding persons in memorization, it is also important to precisely reproduce information whenever it is required, and in this sense, the object cannot be achieved by a tape medium which cannot be randomly accessed or a semiconductor memory which does not provide a sufficient storage capacity. A magnetic disk apparatus is most suitable as a recording medium which meets these requirements, so that it is anticipated that magnetic disk apparatus will be mounted in such recording apparatus and portable information terminals for mobile applications in the future for use in aiding persons in memorization.
In these applications, a magnetic disk apparatus is preferably mounted removably to a storage system such that information collected in the magnetic disk apparatus can be directly processed and/or utilized by a personal computer or the like, an appropriate magnetic disk apparatus can be selectively utilized to demonstrate the performance suitable for the object and cost of a particular application, or a failed magnetic disk apparatus can be readily replaced with a normal one.
A reduction in power consumption is a significant challenge for mounting a magnetic disk apparatus to a mobile device. For addressing this challenge, JP-A-11-259979. JP-A-7-153182, JP-A-11-110917, U.S. Pat. Nos. 5,455,812 and 5,822,288, and the like disclose techniques for limiting the power consumption, taking advantage of a feature of the magnetic disk apparatus which lies in that a data transfer rate between a head and a disk medium of the magnetic disk apparatus is slightly or largely higher than a data transfer rate in an interface between the magnetic disk apparatus and an external device. Specifically, a semiconductor RAM (hereinafter called the “buffer RAM”) is interposed in an information input/output path to the magnetic disk such that information is intermittently transferred between the disk apparatus and buffer RAM, and a spindle motor is stopped and a signal processing circuit is powered off in the disk apparatus when no information is being transferred between the disk apparatus and buffer RAM, thereby saving the power consumption.
An optical disk apparatus, a magnetic disk apparatus or the like incorporates signal processing circuits for compression of information which is written into a magnetic medium, for signal processing such as decompression of read information, for controlling rotations of a spindle motor and movements of heads, and the like. In the aforementioned prior art, the disk apparatus incorporates, in addition to these processing circuits, a buffer RAM interposed in the information input/output path, and processing circuits for controlling intermittent accesses using the buffer RAM, stopping and starting the spindle motor associated with the intermittent accesses, powering the signal processing circuits on and off, and the like.
On the other hand, taking into account the effect of power saving, a buffer RAM having a larger capacity often tends to increase a time in which the magnetic disk is not read or written, i.e., increases the proportion of time in which the spindle motor and the like are stopped, resulting in a larger power saving effect. However, this is true only when a disk apparatus requires sufficiently small standby power consumption during a standby state, in which the spindle motor and the like are stopped, as compared with the power consumed for starting the spindle motor and the power consumed for recording and reproducing information. In a small-sized magnetic disk apparatus for a portable device, less power is consumed for start-up and recording/reproducing operations with a reduction in the size of the apparatus, resulting from a reduction in a disk mass and a windage loss during rotations, a reduction in a spindle motor shaft loss, and the like, so that an increased capacity of the buffer RAM can merely take a minor power saving effect.
As such, when a buffer RAM having a large capacity is required for achieving a large power saving effect, a RAM having such a large capacity should be mounted in each removable magnetic disk apparatus. However, this causes an increased cost of the magnetic disk apparatus. Even when a sufficient power saving effect cannot be achieved by simply increasing the capacity of the buffer RAM, the power saving is desired in any way particularly for a small-sized magnetic disk apparatus.